The present invention relates to a method for adding fats and oils to porous fodder in which the fat and oil are added in a higher ratio to the porous feed containing a great amount of voids formed inside.
Porous feed containing a great amount of voids formed inside are widely known as feeds for pisciculture, etc. As feeds for pisciculture, powders composed solely of fish powder, live fish, pupa etc., kneaded materials thereof, and in addition, pellet type solid feeds etc., processed in the form of solids from compositions prepared by compounding components such as a fish powder, live fish and other components such as vegetable oil cake, cereal powder, starch, vitamins, minerals etc., have been widely used in view of its easy handling, excellent feed making property, etc.
However, solid feeds produced by using a pellet mill etc., have a notable tendency to precipitate and to quickly precipitate once thrown into water. Therefore, such solid feeds are not easily and sufficiently ingested by fish and go rotten at the bottom of water and become causes of water pollution and the generation of sick fish.
For eliminating such defects in solid feeds, there have been produced and used porous feed having floating properties obtained by forming a great amount of voids in pisciculture feed. This porous feed is produced by foaming for a porous structure due to quick vaporization of water when a raw material prepared by compounding various components for feed is kneaded by an extruder and a raw material made into a paste formed by compression heat and pressure in the extruder is extruded into air. Thus produced porous feed floats on a water surface for a long period of time due to a great amount of voids therein and is ingested by fish successfully, and further, is not broken up by water absorption. Therefore, this feed has merits in that it causes little water pollution, etc.
Further, porous feed has been used having high fat and oil content prepared by allowing the above-described porous feed to contain fats and oils in a high ratio since they provide a high growth rate as feeds for pisciculture of young yellowtail, red sea bream, horse mackerel etc.
Conventionally, for adding of fats and oils to porous feed, a raw material prepared by compounding given various components is molded into porous feed by an extruder, then, this feed is dried by a drier utilizing hot air to control the water content thereof, cooled by a cooler, transported to a fat and oil adding apparatus, where fat and oil are added to the porous feed. However, the content of the fat and oil in this case is at most about 15%.
On the other hand, for adding fat and oil in high content, Japanese Laid-Open Patent Publication No. Hei-2-138944 discloses a method in which porous feed is placed under reduced pressure to allow liquid fat and oil to impregnate into the feed. Namely, it is described that porous feed is put into an oil bath and subjected to reduced pressure, however, more efficient production is desired.
The present invention has been accomplished in view of the above-described problems, and an object thereof is to provide a method for adding fat and oil by which a great amount of fat and oil are continuously adhered efficiently on porous feed. The present invention for solving the above-described problems is a method in which porous feed is continuously poured into a fat and oil adding apparatus under reduced pressure together with fat and oil to be added and treated.
As the fat and oil adding apparatus by which fat and oil are continuously added to porous feed while maintaining a reduced condition inside the apparatus, a drum mixer type fat and oil adding apparatus which has conventionally been used or a paddle mixer type fat and oil adding apparatus may be permissible irrespective of mixing type provided reduced condition inside thereof is maintained. Specifically, the entire fat and oil adding apparatus is accommodated and used in a pressure vessel, a rotary valve, a double damper etc., and supply and discharge of porous feed are continuously conducted while maintaining a reduced condition. In this case, it is preferable to use a rotary valve to continue supplying and discharging smoothly.
Regarding the fat and oil adding apparatus, it may be advantageous to use a cylindrical casing in a continuous mixer of a ribbon screw type and to use rotary valves at a supplying port and a discharging port. This mixer has excellent pressure resistance, and can allow addition of fat and oil to be conducted evenly over the whole feed since it is in the form of a cylinder. Further, production is also relatively simple. As the supplying apparatus of fat and oil, a conventional continuous quantitative supplying apparatus may be advantageously placed near the inlet of the fat and oil adding apparatus and thus there is no need to use a special apparatus. Further, the vacuum pump for producing a reduced condition in a fat and oil adding apparatus is not limited by the types thereof.
Alternatively, it may also be permissible that continuous type fat and oil adding apparatuses are placed in multi-stages and addition of fat and oil to porous feed repeated.
Further, in the present invention, a fat and oil adding apparatus may be placed directly after a drier, a cooler may be placed after the fat and oil adding apparatus, and fat and oil are added to porous feed by the fat and oil adding apparatus before the porous feed is cooled.
After being dried by the drier, the product can be modified by given fat and oil addition ratios by passing the product through a continuous fat and oil adding apparatus kept at a reduced condition whether or not the product is one which is cooled by a cooler or a porous feed at high temperature directly after the drier. Particularly if porous feed at high temperature is not cooled and passed through the fat and oil adding apparatus kept at a reduced condition, the volume of a cooler plated in a latter stage can be suppressed since then water is dispersed and evaporated from the porous feed at a high temperature and water content accordingly decreases, and consequently, water content and temperature simultaneously decrease while maintaining the same fat and oil adding ratio. In this case, the volume of the vacuum pump is increased by the vaporization volume of water, for maintaining a reduced condition. Further, there is also a case in which treatment for allowing a rotary valve to have heat resistance is necessary. Moreover, measurements such as keeping moisture etc., may be conducted to prevent dew formation etc., on the mixer casing.
The addition ratio of fat and oil can be improved also by maintaining a reduced condition to a certain extent in a fat an oil adding apparatus, and when it is from xe2x88x92400 to xe2x88x92700 mmHg, the addition ratio can be higher. When the degree of vacuum is lower than xe2x88x92400 mmHg, greater improvements in the addition ratio are not obtained, and even when the degree of vacuum is increased over xe2x88x92700 mmHg, further increases in the addition ratio are not obtained and equipment, such as a pressure resistant apparatus etc., becomes large, therefore such degrees of vacuum are not practical.
Regarding additions of fat and oil to porous feed, the content of fat and oil contained in a raw material itself is from 5 to 10%, the content of fat and oil added before granulation is from 5 to 10%, or more, and the content of fat and oil added by a fat and oil adding apparatus is from 5 to 10%, therefore, the total fat and oil addition ratio of the final porous feed is from 15 to 30%.